Resilient mat construction



Sept. 12, 1961 R. L. MITCHELL RESILIENT MAT CONSTRUCTION 2 Sheets-Sheet 1 Filed OGC. 17, 1957 INVENTOR meer l. /W/c/LL B 6 aiya/72e .5

Sept. 12, 1961 R. L. MITCHELL 2,999,431

RESILIENT MAT CONSTRUCTION Filed Oct. 17, 1957 2 sheets-sheet 2 43 18 55 4f o je 36 37 fg' 6 r :um `l I if 44 42 Q'ng O L 253496) 55 .7 36 o@ be sa 1o l E f2 -l 1"' I i i9 5 56 NVENTOR.

BEM

United States Patent' lO 2,999,f431 RESILIENT MAT CONSTRUCTION Robert L. Mitchell, 2130 San Fernando Road,

' Los Angeles 65, Calif.

Filed Oct. 17, 1957, Ser. No. 690,870 8 Claims. (Cl. 94-13) `This invention relates generally to shock absorbing coverings for lioor and ground surfaces, and more particularly to resilient mats formed from an assembly of individual pads. This application is a continuation-inpart of copending application Serial No. 632,871, filed January 7, 1957, and entitled Resilient Mat Construction, now abandoned.

The `need for shock-absorbing surface coverings is found principally in school yards and playgrounds. In these areas rsevere injuries have been caused to children by falling from play apparatus onto a hard ground surface. As a result, elorts are being made in many cities to. nd a surface covering for playgrounds which will give protection against such injuries.

Various types of surface coverings have been suggested as a solution to the problem, including mats made of resilient material, but none, prior to -this invention, has been truly satisfactory.

A ymajor difliculty encountered in these suggested coverings is that those which have suflicient resilience to give effective protection to a small child falling from a relatively low height do not have suiiicient shock-absorbing capacity to protect a large child falling from a greater height. In other words, the shock absorption range of the coverings is too limited. Also, if the coverings are excessively resilient, they are not firm enough to provide the desired footing for walking and running.

To provide a surface covering which may be easily adapted to different sized areas, it has been further suggested that a resilient mat made up of an assembly of individual pads be used. It has been found, however, that such construction, although advantageous from the standpoint of versatility, raises considerable diliiculty with regard to holding the assembly of pads together. Such mats are extremely vulnerable to separation of the individual pads at their junctions because of the heavy wear and tear to which they are necessarily subjected.

Some further difficulties experienced in surface coverings of this type are that the coverings crack, stiften, or otherwise rapidly deteriorate when continuously exposed to the weather, are not sufliciently durable to withstand lthe `heavy usage given to such a surface, or are too expensive to be practical.

It is therefore a major object of this invention to pro vide a resilient mat for use as a surface covering which gives eifective protection against injuries to persons falling thereon over a wide range of shock magnitudes and is sufiiciently iirm to assure a good footing for walking and running; these advantageous characteristics are due largely to a multi-stage shock absorbing facility incorporated into the mat.

It is also an important object of the invention to pro.- vide a resilient mat of the type described above winch consists of an assembly of individual resilient pads which are interlocked together in such a manner as to avoid any injunction between pads extending in a straight unin- Yterrupted line across the mat. This special interlocking arrangement establishes a secure connection between the individual pads without the use of lany external bonding aids, such as adhesives, makes separation of the pads virtually impossible during normal use of the mat, and yet permits disassembly of the mat when desired. Also, the pad assembly type construction allows the mat tobe shaped to any desired area.

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Another object of this invention is to provide a resilient mat of the type described above which has a wedge-V shaped ramp border to prevent persons from catching their feet on the edge of the mat and tripping themselves or uprooting the mat.

A further object of this invention is to provide a resilient mat of the type described above which has releasable anchor means associated with its border which positively attach the mat to the covered surface and thus prevent'l its being moved or uprooted.

Still another object of this invention is to provide a method and apparatus by the use of which the abovementioned releasable anchor means may be formed into the mat in such a way as to make tearing loose ofthe anchor means virtually impossible.

Still a further object of this invention is to provide a resilient mat of the type described which can be economi` cally molded from material which is extremely durable and will withstand continuous exposure to the Weather without losing its beneficial properties.

These and other objects and advantages of this invention will become apparent from the following detailed description of a preferred embodiment thereof and from and inspection of the accompanying drawings, in which:

FIGURE 1 is a partial plan view of a mat embodying the invention;

FIGURE 2 is an enlarged plan View of one of the pads used in the mat shown in FIGURE l;

FIGURE 3 is a sectional elevational view taken on line 3--3 in FIGURE l, showing, in particular, the border of the mat;

FIGURE 4 is an enlarged, partially sectioned plan view taken at area 4 in FIGURE 1 and showing a junction be- -tween the pads in the mat;

FIGURE 5 is an enlarged sectioned plan view taken at area 5 in FIGURE 1, and showing the junction between two pads at the border of the mat;

FIGURE 6 is an enlarged sectional elevational view taken on line 6-6 in FIGURE 7 and showing the releasable anchor means;

FIGURE 7 is a partially sectioned plan view of a portion of the mat showing the releasable anchor means;

FIGURE 8 is a sectional elevational view showing the molding apparatus used to form the releasable anchor means into the mat;

FIGURE 9 is an enlarged sectional elevational view of the mat taken at 9 9 in FIGURE 7; and

FIGURE l0 is a perspective view of a plate used as a portion of the releasable anchor means.

Referring now to the drawings, and particularly to FIGURE 1 thereof, the numeral 10 designates a mat embodying the invention. The mat is disposed in covering relationship on a surface 11 and is made up of an assembly of interlocked pads 12. The pads 12 are molded from a resilient, durable, weather-resistant material such as a rubber composition or synthetic rubber product. It will be understood, of course, that other materials with suiircient resiliency, durability, and weather resistance may be used, if desired, such as certain plastic materials.

The pads 12 which make up the mat 10 are of several different types, depending upon their use in the mat. The principal portion of the mat is formed by main pads 13 which are shaped like `a cross (see FIGURE 2). These main pads 13 have alternating T-shaped tongues and slots, 14 and 15 respectively, formed in their edges about their complete periphery. These tongues and slots 14 and 15 interlock with tongues and slots on adjoining pads to connect the pads together and form the mat 10, as ywill be explained later.

When formed into an assembly, a main pad 13 adjoins and connects to other pads at each of its four ends.

Patented Sept. 12, 1961,

Due to the main pads 13 being cross-shaped, however, square voids are formed at every junction of four main pads (see FIGURE 1). To fill these voids, square connector pads 16 are provided. These connector pads 1o also have alternating T-shaped tongue and slots A14 and 15 formed in their edges about their complete periphery which interconnect them to the adjoining mainpads 13.

Two other types of pads 12 are necessary to complete the mat 10. These are side pads 17 and corner pads 18. Three of the four edges of the side pads 17 adjoin other pad's and have tongue and slots 14 and 15. the fourth edge forms a portion of a straight line border 19 on the mat 10. rThe border 19 is a wedge-shaped ramp which tapers the upper surface of the mat down to meet the supporting surface 11 (see FIGURE 3). The edge of Side pad 17 opposite the edge having the Iborder portion 19 is contoured to tit the edges of two interconnected main pads 13 and to overlap their junction. The other two edges of the side pads are contoured' in a straight line and' are joined with like edges of other side pads or corner pads.

The corner pads 18 have two edges which form a right angle corner on the mat 1.0 between two of the straight line borders 19. These edges also form part of the border 19 and are therefore wedge-shaped ramps as described f above. The other two ed'ges of the corner pads 1S are contoured to adjoin side pads from each of the two intersecting borders 19 and a corner of an adjacent rnain pad 13. These latter edges each overlap junctions between the main pad and the two side pads and have tongue and slos 14 and 15, which interlock with these adjoining pa s.

Fromk this description and by reference to FIGURE 1 it will be understood that by proper interrelation and disposition of the four types of pads 12, the pads may he assembled together to form the mat 1h. It will also be understood that the mat 10, when properly formed by the pads 12, will he surrounded by the wedge-shaped ramp border 19 so that the possibility of persons tripping on or uprooting the edges of the mat is reduced to a minimum.

Though four types of pads 12 are used to make up the mat 10, the pads themselves have great individual versatility. For example, the main pads 13 and connector pads 16 are symmetrical so that they malte exactly the same iit regardless of which. edge is disposed upward. Also, any pad of a certain type, as for instance, a corner pad 18, may be interchanged with any other pad of'the same type. Y

To prevent the mat 1t! from being separated at the junctions between the pads 12 by wear and tear, the junction between any two pads is overlapped or extended across and secured by a third pad. This is best seen by reference to FIGURE 4 where the lower end of one main pad 13a is joined to the upper end of another main pad 13b and a junction 30 formed thereby is overlapped by one edge of a connector pad 16a. Because of the positions of the tongues and slots 14 and 15 on the three associated pads, the overlapping connector' pad 16a forms a. connection which bridges the junction 3d and holds it against separation. The connection consists of the tongue 14a which engages main pad 13a in the slot 15a, the tongue 14b which engages the main pad 13b in the slot 15b, and the connector pad 16a itself which contains these two tongues.

form into an uninterrupted line completely across the mat.v In fact, none of the junctions in the mat 10 extends for a greater distance than the width of one'padV without encountering an offset. The mean line referred to above may also be defined as the straight line passing through those points on the tongues which are half way out from the edge of the mat or, equivalently, which are half way out from the innermost part of the groove to the outermost part ofadjacent tongues.

The only junctions which are not clamped at both ends by an overlapping pad are those between the pads which contain portions of the border 19. These junctions intersect the border at one end and therefore cannot be overlapped or extended across by another pad at that end. This difliculty is overcome, however, by providing a border cable 31 which is'rnolded into each of the side pads 17 and' corner pads 18. The cable 31 extends into a small opening 32 at the edges of these pads adjacent the border portion and a connector 33 is provided which ts inside of the openings 32 and joins the cables of adjacent pads. This secures the junctions between the border containing pads at both ends just like the other ,junctions inthe mat, and thus renders the mat practically invulnerable to separation.

The cable 31 and connectors 33 are completely cov.- ered by the mat during normal use so that they cannot cause any injury to persons using the mat. Also, the connectors may be disconnected, when desired, to allow disassembly of the mat.

It will be appreciated that many other arrangements could be used to hold the pads together at the border such as wire clamps, threaded sleeves and screws and others. been found to be quite satisfactory for this purpose.

To further assure that the mat will not be uprooted at the border 19 and to prevent the mat from sliding about on the covered surface, anchor means 35 are provided in each of the pads forming a portion of the border. The anchor means 35 comprises a rigid plate 36 which s molded into the pads medially of their depth Iand ananchor bolt 37. The plate 36 is disposed approximately horizontal and covers a sufficiently large area to make it, in effect, an integral part of the pad. To increase the strength of the bond between the plate 36 and the pad, a plurality of holes 38 are formed in the plate, as shown in FIGURE 10. These holes 38 are of suil'lcient size so that during molding the pad material ows through the holes 'and forms lingers 39. 'Since the fingers 39 connect the material on each side of the plate 36, they interlock the plate with the pad (see FIGURE 9).

The plate 36 also has an opening 40 approximately at its 'center which registers with an opening 41 formed in the pad above the plate 36 and an opening 42 `formed in the pad below the plate. The anchor boltA 37 is passed through these openings. The opening 41 is large enough in diameter to freely pass the head 43 ofthe anchor bolt', however, the opening 40 through plate 36 is onlylarge enough to pass the shank 44 of the anchor bolt 37. The bolt head 43 therefore engages the plate 36 adjacent the opening 40. The opening 42 below the plate 36l is ap -proximately the same size as the opening 40.

To secure the mat 1t) to the surface 11, a wedge and nut device 45 is provided. 'This device is ii'rst driven into the surface in alignment with the anchor bolt 37, andthe anchor bolt is then tightened into the nut. The wedge and nut device 45 is constructed so that when the anchor bolt draws upwardly on the nut, the wedge spreads forming a secure engagement with the surrounding substance. The anchor bolt 37 is therefore securely held by the wedge and nut device 45 and, through its engagement with the plate 36, rmly anchors the pad and mat tov the covered surface.

In order to mount the plate 36 of the anchor means in the pads of the matduring molding so that the plate becomes an integral part of the mat, a specialgmethod and apparatus are used (see FIGURE 8). By use of this method and apparatus, the'plate 36 is held ixedlin the cavity of the mold substantially medially of the The cable and connectors used, however, havewhile the pad material is owed around it and formed irto a pad with openings 41 and 42 aligned with opening To perform this feat, the pads are molded face do-wn in a mold having a lower section 47 and an upper section 48. The openings 41 and 42 are formed by an elongated center stem 49 which is mounted on lower section 47 and extends vertically upward therefrom. The stem 52 has a larger diameter than the plate opening 49 at its lower portion 50 and a diameter equal to opening 40 at its upper portion 51. A horizontal shoulder 52 is provided on the stem 49 at the junction of its two portions. When the plate 36 is disposed in the mold cavity the upper portion 51 of steam 49 is passed through opening 40 so that the shoulder 52 engages the plate adjacent the opening and provides support for the plate at its center.

To support the plate 36 at its extremities and prevent it from tilting or rotating, vertically directed pins 53 `are provided on the lower section 47, three at each end of the plate. One of the pins 54 at each end is longer than the other two and extends through a hole 55 in the plate. The other two pins are pointed and lit into corresponding indentations 56 in the plate. The plate is thus prevented from tilting by the two shorter pins and is held against rotation by the longer pins.

The method used to mold a pad with plates 36 integral therewith is as follows. The lower mold 47 is first set up with the proper number of stems 49 and pins 53 for the number of plates required, i.e. usually two plates in a corner pad 18 and one in a side pad 17, and the plates are mounted thereon. Then the pad material is placed'in the lower section 47 and lthe upper section 48 is lowered into position to close the mold. =Heat is then applied to the mold and as the material becomes liquefied it surrounds the plates 36, and flows through the holes 38 to form the lingers 39. When the material has been properly shaped and conditioned, sections 47 and 48 of the mold are separated and the newly formed pad is ejected from the mold in the usual manner, the plate 36 remaining fixed in the pad, while stems 49 and pins 53 are withdrawn therefrom and remain attached to the mold.

iTo provide a relatively smooth and even upper surface for the mat 10, the upper portion of the'pads 12 comprises a solid surface layer 22. This surface layer 22 is thick enough to be relatively rigid and therefore helps to provide a firm footing for persons walking or running on the mat. The solid layer 22 also presents an extremely durable surface with respect to Wear and weather.

In order to give the mat 1t) the necessary range of shock absorbing ability to adequately protect persons falling thereon from injury, the pads 12 are equipped with a shock absorbing facility having two stages. The first stage of the shock absorbing facility of the pads 12 is provided by a plurality of rectangular pockets 23 which are disposed on the under side of the surface layer 22. These pockets 23 are formed by a series of parallel ribs 24 which are molded integral with and perpendicular to the under side of the layer 22 and a series of parallel cross-ribs 25 which are also molded integral with the underside of the layer 22 in the same manner as the ribs 24 but perpendicularly intersect the ribs.

The ribs 24 and cross-ribs 25 have the same vertical depth so that both share in supporting the surace layer 22 when the pads are resting on a relatively even surface. Also, since the ribs and cross-ribs, 24 and 25, `are of equal depth, the pockets 23 have coplanar lower edges. This gives the pockets a suction cup characteristic which enables them to establish a connection with the surface covered by the pads and thereby assist in holding the mat to the surface.

The second stage of the shock absorbing facility of the pads 12 is provided by a series of elongated supports 26 and cross-supports 27. These supports and cross-supports are also formed integrally with and perpendicular to the under side of the layer 22 in the same manner as the ribs and cross-ribs. The supports 26 are disposed para` allel to the ribs 24 with the supports 26 mounted midway between each pair of ribs, while the cross-supports 27 are disposed parallel to the cross-ribs 25 and mounted midway between each pair of cross-ribs. The supports and cross-supports 26 and 27 are substantially shorter vertically than the ribs and cross-ribs 24 and 25, however, s0 that when the pads 12 are resting in their normal condition on the surface 11, only the ribs and cross-ribs are in contact with the surface.

The shock absorbing facility operates as follows. When a relatively light shock spread over a substantial area strikes the surface layer 22, such as the foot of a person running, the Iribs and cross-ribs 24 and 25, because of their edgewise disposition, support the relatively inliexible surface layer 22 like rigid structural braces, allowing very little give. The pad, therefore, presents a firm surface to such contact. lf, however, a shock Aof slightly greater magnitude, or one concentrated in a smaller area strikes the mat 1d, the ribs and cross-ribs 24 and 25, are bent from their vertical planes to the extent that they lose the relative -rigidity accorded by their edgewise disposi-tion and are compressed vertically until the shock is absorbed. This, of course, brings the supports and cross-supports 26 and 27, downward closer to the covered surface 11. So long as the shocks do not sufficiently compress the ribs and cross-ribs to bring the supports and cross-supports into contact with the surface 11 they are absorbed by the action of the ribs and cross-ribs alone. These conditions constitute the first stage of shock absorption.

When, however, a still greater shock strikes the mat itl', that is, one which is quite severe either in magnitude or concentration, and the ribs 24 and cross-ribs 25 are bent and compressed to such an extent that the supports 26 and cross-supports 27 are forced into contact with the surface 11 and are themselves bent and vertically compressed. These conditions constitute the second stage of shock absorption. Since during the second stage of shock absorption all four ofthe rib members, that is, the ribs 24, cross-ribs 25, supports 26 and cross-supports 27 are utilized in absorbing the shock, the mat 1.6 presents greater `resistance to the shock during this stage thereby increasing the mats shock-absorbing capacity. This second stage is still, however, considerably softer than the surface 11 alone or covered only by the solid layer 22.

The advantage of the greater resistivity of the second stage is that shocks which would normally force the layer 22 into contact with the surface 11 if resisted only by the ribs 24 and cross-ribs 25 will be prevented from doing so because of the additional resistance supplied by the supports 26 and cross-supports 27. Therefore, by use of -a second stage which has a greater resistivity to shocks than the rst stage, it is possible to provide a mat which is soft enough to give good protection to light shocks and still has suflicient shock-absorbing capacity to give protection to large shocks also.

From the above explanation of the shock-absorbing facility of the mat 10, it will be appreciated that more than two stages can be used if desired and the ribs, supports and pockets may be of many different shapes and arrangements Understanding lthe structure and operation of -a preferred embodiment of the invention because of the twostage shock absorption facility which gives protection over a wide range of shock magnitudes and the special interlocking arrangement -Which makes the pads virtually invulnerable to separation, the invention represents a significant improvement in protective coverings for pl-aygrounds. A protective covering embodying this invention, such Ias the mat l@ also provides a rm surface to assure the proper footing, is easily adapted to any desired area, and may be readily disassembled, if desired, `for storage or transport. In addition, the pockets 23 form :a suction grip with the surface 11 to hold the mat in place and the ri Wedge-shaped ramp border 19 protects the edges of the mat against uprooting.

While the form of the invention herein shown and described in detail is fully capable of achieving the objects and prow'ding the advantages hereinbefore stated, it is primarily illustrative of a presently preferred construction.

I claim:

l, A mat comprising: a plurality of resilient pads assembled to form a layer having a relatively smooth and even upper surface, said pads having protruding turns thereon, having spaced alternating tongues and slots of like shape yformed `along the periphery of said with said tongues having lateral projections, said pads being connected together along adjacent edges to `form rows with a tongue of one interlocking with an adjacently positioned slot on an adjacent pad whereby is formed a line of junction between adjacent pads, said line of junction thereby being spaced apart from re-occurring interlocked lines of junction between other adjacent interlocked pads, a projecting arm on another adjacent pad connecting with the adjacent arms of two adjacent connected pads and extending transverse to the junction line thereof to form a connecting means yat the end of the line of junction Afor `securing said two adjacent connected pads together, a first set of orthogonally intersecting rib shock-absorbing means Iformed integral with said layer and disposed to absorb the initial force of a shock applied to said layer; and a second set of orthogonally intersecting rib shock absorbing means formed integral with said layer and disposed alternately between said first set and being of a lesser height than said lirst set to supplement said first means by absorbing the force of any shocks which stress said irst means to near its limit of absorption, whereby said first and second sets of shock-absorbing means are substantially uniformly disposed in said mat.

Z. A mat comprising: a plurality of resilient pads assembled into a layer having a relatively smooth and even upper surface and a peripheral border, said pads comprising cross-shaped main pads having projecting arms and a relatively smooth and even upper surface and alternating tongues and slots of like shape formed in their peripheral edges with said tongues having 4lateral projections, said main being arranged in rows and being interconnected with each other in end to end relationship at the ends of the arms of the cross and resilient square-shaped connector pads having a relatively smooth and even upper suriace and alternating tongues and slots similar to those on said main pads and being interconnected between said main pads in the voids left when said cross-shaped main pads are interconnected such that the junctions between said interconnected main pads are transversely overlapped at the end by said connector pads thereby forming a connection which bridges said junctions; securing means disposed adjacent said border at the junctions between pads containing portions of said border for holding said border containing pads against separation at said border junctions; a plurality of resilient ribs formed integral with the underside of said upper sur-tace of said pads and their tongues and perpendicular thereto, said ribs being disposed parallel to each other; `a plurality of resilient crossribs formed integral with the underside of said upper surface and perpendicular thereto, said cross-ribs eing disposed parallel to each other and perpendicular to said ribs, and being of substantially the same depth as said ribs whereby said ribs and cross-ribs form -a plurality of pockets on the underside of said surface; a plurality of resilient supports formed integral with the underside of said upper surface and perpendicular thereto, said supports being disposed parallel to said ribs approximately midway therebetween and being less in depth than said ribs and cross-ribs; and a plurality of resilient cross-supports formed integral with the underside of said upper surface and perpendicular there-to, said cro-ss-supports being disposed parallel to said cross-ribs approximately midway therebetween and being of the same depth as said supports whereby said pockets formed by said ribs and cross-ribs are subdivided into smaller pockets by said supports `and cross-supports at their uppermost portions.

3. A mat comprising: a plurality of resilient crossshaped main pads having projecting `arms and a relatively smooth and even upper surface and alternating tongues and slots of like shape formed in their peripheral edges with said tongues having lateral projections, said main pads being arranged in rows and being interconnected with each other in end to end relationship at the ends of the arms of the cross; a plurality of resilient squareshaped connector pads having an upper surface and alternating tongues and slots similar to those on said main pads and being interconnected between said main pads in the voids left when said cross-shaped main pads are interconnected such that the junctions between said in-. terconnected main pads are transversely overlapped at the end by said connector pads; a plurality of resilient side pads with an upper surface similar to said main pads but having a wedge-shaped ramp border on the other peripheral edge and alternating similar tongues and slots on the other peripheral edges, said other edges being interconnected to two other side pads and two interconnected. main pads such that said side pads extend across an end of the junction of the adjacent arms of said associated main pads and said associated main pads extend across ends of the junctions between said side pads; a plurality of corner pads with an upper surface similar to said main pads and having a wedge-shaped ramp border on two adjoining peripheral edges and alternating tongues and slots on the other peripheral edges, said other edges being interconnected to two side pads and a main pad such that the adjacent arms of said main pad extend across ends of the junctions between said corner pads and side pads; said pads being interchangeable such that each pad may be interchanged with any other pad of its same type and said alternating tongues and slots being so arranged on said pads that wherever one pad extends across an end of the junction between two others as aforesaid a connecting means is formed by said last named pad which connecting means holds said junction against separation; securing means disposed adjacent said border at the junctions between the pads containing portions of said border for holding said border containing pads against separation at said border junctions; a plurality of resilient ribs formed integral with the underside of said upper surface and perpendicular thereto, said ribs being disposed parallel to each other; a plurality of resilient cross-ribs formed integral with the underside of said upper surface and perpendicular thereto, said crossribs being disposed parallel to each other and perpendicular to said ribs, and being of substantially the same depth as said ribs, whereby said ribs and cross-ribs form a plurality of pockets on the underside of said surface; a plurality of resilient supports formed integral with the underside of said upper surface and perpendicular there` to, said supports being disposed parallel to said ribs ap-J proximately midway therebetween and being substantially less in depth than said ribs and cross-ribs; and a plurality of resilient cross-supports formed integral with the underside of said upper surface and perpendicular thereto, said cross-supports being disposed parallel to said cross-ribs approximately midway therebetween and being of the same depthas said supports whereby said pockets formed by said ribs and cross-ribs are subdivided into smaller pockets by said supports and cross-supports at their uppermost portions.

4. A mat comprising: a plurality of pads assembled into a layer; a first set of said pads consisting of crossshaped main pads having a relatively smooth and even upper surface and alternating tongues and slots of like shape with said tongues having lateral projections formed along their peripheral edges and lying along `a mean line passing through the mid point of said tongues and slots, said main pads Ibeing interconnected with each other at the ends of the arms of the cross to form rows by intertting corresponding male and female tongue and slot portions of adjacent pads so that the mean line of adjacent pads coincide; a second set of said pads consisting of generally square-shaped connector pads having the same thickness as said main pads and having a smooth upper surface, alternating tongues and slots similar to those on said main pads being on the peripheral edges of said connector pads to interconnect said connector pads between said main pads in the voids left between the arms of adjacent main pads when said cross-shaped main pads are interconnected with each other in rows; said square-shaped connector pads thereby forming a junction with the arms of adjacent main pads which overlap the junction between said main pads and forms a T joint therewith; said plurality of pads being arranged in a pattern such that one such T joint is formed at the mid point of each side of-each of said square connector pads; said arrangement of T joints being such that when said plurality of pads are thus assembled in contiguous relation the mean line of each of the junctions therebetween is zig-zag and thus does -not form an uninterrupted line across said layer, a plurality of resilient ribs of equal length formed integral with the underside of said upper surface of said pads and their tongues and perpendicular thereto and forming a first set of shock absorbing ribs for pressure applied to the surface of the mat and a plurality of resilient ribs shorter than said rst set of ribs and intermediate said first set of ribs and formed integral with the underside of said upper surface and forming a second set of shock absorbing ribs to supplement said irst set of shock absorbing ribs by absorbing the force of any shocks which stress said rst set to near its limit of absorption whereby a substantially uniform resilient shock absorbing means is formed in said mat.

5. A mat comprising: a plurality of resilient crossshaped main pads having projecting arms and a relatively smooth and even upper surface and alternating tongues and slots of like shape formed in their peripheral edges with said tongues having lateral projection, said main pads being arranged in rows and interconnected with each other at the ends of the arms of the cross; a plurality of resilient square-shaped connector pads having an upper surface and alternating tongues and slots similar to those on said main pads -and being interconnected between said main pads in the voids left when said cross-shaped main pads are interconnected such that the junctions between said interconnected main pads are transversely overlapped at the end by said connector pads; a plurality of resilient side pads with an upper surface similar to said main pads but having a border on the outer peripheral edge and alternating similar tongues and slots on the l other peripheral edges, said other edges being interconnected to two other side pads and two interconnected main pads such that said side pads extend across an end of the junction of said associated main pads and the adjacent arms of said associated main pads extend across ends of the junctions between said side pads; a plurality of corner pads with an upper surface similar to said main pads and having a border on two adjoining peripheral edges and alternating tongues and slots on the other peripheral edges, said other edges being interconnected to two side pads and a main pad such that the adjacent arms of said main pad extend across ends of the junctions between said corner pads and side pads; said pads being interchangeable such that each pad may be interchanged with any other pad of its same type and said alternating tongues and slots being so arranged on said pads that wherever the adjacent portion of one pad extends across an end of the junction between two others as aforesaid a connecting means is formed by said last named pad which connecting means holds said junction against separation; a plurality of resilient ribs of equal length formed integral with the underside of said upper surface of said pads and their tongues and perpendicular thereto and forming a rst set of shock absorbing ribs for pressure applied to the surface of the mat and a plurality of resilient ribs shorter than said first set of ribs and intermediate said lirst set of ribs and formed integral with the underside of said upper surface and forming a second set of shock absorbing ribs supplemental to said tirst set of shock absorbing ribs whereby said first and second sets of ribs are substantially uniformly disposed in said mat.

6. A mat according to claim 5 including anchoring means in at least the border of a side pad, said anchoring means comprising a plate disposed in one of said side pads medially of the width thereof, a passage through said pad and plate, a bolt disposed in said passage and engaged with said plate, and means on the surface covered by said mat for engaging said bolt to anchor said pad to said surface.

7. A mat comprising; a plurality of resilient crossshaped main pads having projecting arms and a relatively smooth and even upper surface and alternating tongues and slots of like shape formed in their peripheral edges with said tongues having lateral projections, said main pads being arranged in rows and being interconnected with each other in end to end relationship at the ends of the arms of the cross; at least one resilient square-shaped connector pad having an upper surface and alternating tongues and slots similar to those on said main pads and being interconnected between said main pads in the void left when said cross-shaped pads are interconnected such that the junctions between said interconnected main pads are transversely overlapped at the end by said connector pad; at least one resilient T-shaped side pad with an upper surface similar to said main pads and having a border on the outer peripheral edge and alternating similar tongues and slots on the other peripheral edges, the other adjacent edges being interconnected to adjacent main pads such that the side pad there adjacent extends across the end of the junction of said associated main pads; a plurality of corner pads of L-shape with an upper surface similar to said main pads and having an outer peripheral border on two adjoining peripheral edges and alternating tongues and slots on the other peripheral edges of similar shape to the tongues and slots on the other pads, said other edges of the corner pads being connected to adjacent side and main pads such that the adjacent arms of said main pads extend across ends of the junctions between said corner and side pads; said pads being interchangeable such that each pad may be interchanged with any other pad of its same type and said alternating tongues and slots being positioned on said pads that whenever one pad extends across an end of the junction between two others as aforesaid a connecting means is formed by said last named pad which connecting means holds said junction against separation; a plurality of resilient ribs of equal length formed integral with the underside of said upper surface of said pads and their tongues and perpendicular thereto and forming a first set of shock absorbing ribs for pressure applied to the surface of the mat and a plurality of resili-l ent ribs shorter than said first set of ribs and intermediate said first set of ribs and formed integral with the underside of said upper surface and forming a second set of shock absorbing ribs to supplement said first set of shock absorbing ribs by absorbing the force of any shocks which stress said first set to near its limit of absorption, said rst and second sets of ribs being substantially uniformly disposed in said mat.

8. A mat comprising; at least two resilient cross-shaped main pads having projecting arms and relatively smooth and even upper surface and alternating tongues and slots of like shape formed in their peripheral edges with said tongues having lateral projections said main pads being arranged in a row and being interconnected with each other in end to end relationship at the ends of two adjacent arms; a resilient T-shaped side pad with an upper surface similar to said main pads and having a border on the outer peripheral edge formed by the outer surface of the cap portion of the T-shaped pad and alternating similar edges and alternating tongues and slots on the other pe- 1 ripheral edges of similar shape to the tongues and slots on the other pads, said other edges of the corner pads being connected to adjacent side and main pads such that the adjacent arms of said main pads extend across ends of the junction between said corner and side pads; said pads being interchangeable such that each pad may be interchanged with any other pad of its same type and said alternating tongues and slots being positioned on said pads that whenever one pad extends across an end of the. junction between two others as aforesaid a connecting means is formed by said last named pad which connecting means liolds said junction against separation; a plurality of resilient ribs of equal length formed integral with the underside of said upper surface of said pads and their tongues and perpendicular thereto and forming a iirst set of shock absorbing ribs for pressure applied to the surface of the mat and a plurality of resilient ribs shorter than said first set of ribs and intermediate said rst set of ribs and formed integral with the underside of said upper surface and forming a second set of shock absorbing ribs to supplement said iirst set of shock absorbing ribs by absorbing the force of any shocks which stress said first set to near its limit of absorption, said first and second sets of ribs being substantially uniformly disposed in said mat.

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